1. Technical Field
The present invention relates to a white light emitting phosphor and a light emitting module using the same, and more particularly to a phosphor for emitting a white light without using phosphors for emitting lights having other colors, and a light emitting module using the same.
2. Background Art
There has been developed an irradiation light source in which mercury is not used in respect of environmental issues and power saving considerations, and in which a light emitting diode (LED) or a semiconductor laser (LD) is combined as an excitation light source with a phosphor and a light emission at that time is set to be a light source, so that power consumption can be lower.
For example, Japanese Patent No. 2927279 discloses a light emitting diode for wholly emitting a white-color light based on an additive color mixture with a yellow-color light emitted from a Ce-activated rare earth aluminate phosphor that absorbs apart of a blue color light and emits a light. However, this combination type has a drawback that a rate of the blue light (a primary light) emitted from a semiconductor device to the yellow light (a secondary light) emitted from the phosphor is changed depending on a thickness of the phosphor disposed on the semiconductor device, and thus a stable emission spectrum cannot he obtained.
In recent years, in order to solve the above-described problem, a light emitting module in which an ultraviolet light or a visible light of a short-wavelength is set to be a primary light emitted from a semiconductor device and a phosphor having three components of green, blue and red is mixed, is introduced as a method of complementing a drawback caused by a white-color synthesis in a two-color addition. However, there are problems in the following aspects.
i) There are no phosphors for emitting red and green lights efficiently and stably in near ultraviolet rays.
ii) The green and red phosphors with an absorption in a broadband absorb a blue light so that the blue light is emitted unstably and a stable white light cannot be achieved.
iii) At least three types of phosphors of R, G and B are used. For this reason, mixing and dispersing steps are required so that cost is increased as a result.
In order to solve these problems, a composition that emits a white light using one type of phosphor has also been reported in Japanese Unexamined Patent Publication; JP-A-2003-206482. The emission spectra constitute the white light by a two-color mixture of a blue light and a complementary color for an orange color. However, there is a problem as to a luminance and a color rendering property due to a lack of a green spectrum having the highest spectral luminous efficacy.